Power-operated boom structure



May 12, 1964 W. M. PIERCE, JR

POWER-OPERATED BOOM STRUCTURE '7 Sheets-Sheet 2.

Filed April 27, 1960 mm 6% Q? mm mm h -INVENTOR Wayne M. P/erc /r.

Q @anflooM ATTORNEYS W. M. PIERCE, JR

POWER-OPERATED BOOM STRUCTURE May 12, 1964 Filed April 27, 1960 '7Sheets-Sheet 3 1 I I 1 Q #1.. Q Fa I 1 W" H W h I WM UH w K: H Q 1 I I nI 6 on.

w. ,//40 1 Es w U w Q m H M l q. 1 1 K &N\N\ QSW Nm \m h INVENTOR WayneM. P/ercc',J/*.

May 12, 1964 w. M. PIERCE, JR

POWER-OPERATED BOOM STRUCTURE Filed April 27, 1960 7 Sheets-Sheet 4 17Li H INVENTOR Wayne M. Pierce, Jr.

ATTORNEYS May 12, 1964 W. M. PIERCE, JR

POWER-OPERATED BOOM STRUCTURE Filed April 27, 1960 7 Sheets-Sheet 5INVENTOR Wayne I"). P/erce Jr.

WOM c ATTORNEYD May 12, 1964 w. M. PIERCE, JR

POWER-OPERATED BOOM STRUCTURE Filed April 27, 1960 7 Sheets-Sheet 6INVENTOR Wayne M. Pierce, Jr.

ATTORNEY5 United States Patent 3,132,718 PGWER-QPERATED 309MS'ER'UiITURE Wayne M. Pierce, Jzz, Milford, Qomr, assignor to Hunt-Pierce Corporation, Milford, Conn, a corporation of Qonnecticut FiledApr. 27, 196i Ser. No. 24,$55 Claims. (U. 182-63) This invention relatesto articulated boom structures, and relates more particularly to boomstructures, usually carried by trucks, of the type that raise andsupport a workman a distance above the ground. Such structures have beenfound useful for many purposes. For example, they have been employed inthe cutting of high tree limbs and for the construction and maintenanceof overhead electrical lines and allied equipment.

Overhead lines often carry high voltages which present a hazard toworkmen and others near workmen. Heretofore, in the use of suchequipment, difficulty has been encountered in protecting linemen fromsevere, and sometimes fatal, shocks from high voltage electrical linesof the overhead type.

Another difiiculty that has been encountered in the past is that theseboom structures, when constructed to reach substantial heights, have atendency to tip their supports, such as trucks, by their weight whenthey are extended. Obviously, this tendency may be a dangerous one forworkmen unless proper provisions are made to stabilize the trucks. Theuse of long boom sections in an articulated boom structure to attainsubstantial heights has not only resulted in a problem in connectionwith the stowage of these sections on a truck, but has required, in manyinstances, the use of a heavy truck or a truck provided with stabilizingoutriggers which may be used only when the truck is stationary.

One object of the invention is to provide an improved articulated boomstructure for carrying workmen aloft, which is particularly well suitedfor support on a truck for transport from place to place.

A further object is to provide a boom structure having a very highdegree of safety in use, especially safety with respect to electricalshock hazards.

Still another object is to provide a boom structure which has greatstability in use and which, while being able to support a workman at asubstantial height, may be supported on a relatively light truck and maybe sup ported from the truck without the use of truck outriggers to actas stabilizers.

A further object is to provide a boom structure, such as characterizedabove, the parts of which may be folded and easily stowed on a truck.

Another object of the invention is to provide improved means foreffecting movements of the parts of a boom structure such ascharacterized above.

In the accompanying drawings:

FIG. 1 is a broken side elevational view of a truck carrying a boomstructure embodying the invention, the boom structure being shown infolded condition;

FIG. 2 is a rear elevational view of the truck illustrating the upperboom sections in extended condition and showing the amplitude ofswinghig movements obtainable in the boom structure;

FIG. 3 is an enlarged elevational view of the boom structure inpartially unfolded condition, the structure being partially broken awayto better illustrate certain elements;

FIG. 4 is a top plan view of the boom structure;

FIG. 5 is an enlarged sectional view taken on line 5-5 of FIG. 4;

FIG. 6 is an enlarged sectional view taken on line 6-6 of FIG. 4;

FIG. 7 is an enlarged sectional view taken on line 7-7 of FIG. 4;

FIG. 8 is an enlarged sectional view taken on line 8-8 of FIG. 3;

FIG. 9 is a sectional view taken on line 9-9 of FIG. 8;

FIG. 10 is an elevational view partially broken away, illustrating oneof the pneumatic control mechanisms employed in the boom structure;

FIG. 11 is a fragmentary view on a larger scale and taken in the sameplane as FIG. 10, better illustrating certain parts of the controlmechanism, shown in FIG. 10;

FIG. 12 is a sectional view of a slave unit operated by the controlmechanism of FIG. 10;

F 1G. 13 is a fragmentary view illustrating in side elevation certainelements of the boom structure in extended positions, looking from oneside of the truck;

FIG. 14 is a view of the same elements in extended positions, lookingfrom the rear of the truck;

FIG. 15 is a schematic view, illustrating electrical and hydraulicelements which operate the boom structure;

FIG. 16 is an elevational view of a truck-carried boom structure ofmodified form and equipped with an auxiliary boom attachment; and

FIG. 17 is a view of the boom attachment, looking in the direction ofarrows 17 in FIG. 16.

In the form of the truck-mounted boom structure, shown in FIGS. 1through 15, the base portion of the boom structure is indicatedgenerally at A; a turret, mounted on the top of the base portion forswiveling movement on a vertical axis, is indicated generally at B; alower boom section, pivotally mounted on the turret for verticalswinging movement, is generally indicated at C; an upper boom section,pivotally mounted on the outer end of the lower boom section to swing ina vertical plane, is generally indicated at D; and a work platform,mounted on the outer end of the upper boom section, is generallyindicated at E. The turret B is rotatable in either direction withoutlimit, and the boom sections have the amplitude of swinging movementshown in FIG. 2. As shown in this view, the lower boom section C mayswing through an arc of substantially degrees, while the upper boomsection D may swing through an arc of substantially 270 degrees. Ahydraulic cylinder, indicated generally at F, is provided to swing thelower boom section, while a hydraulic cylinder, indicated generally atG, is provided to swing the upper boom section. Electric motor (see FIG.8) and gearing means, indicated generally at H, is provided to rotatethe turret on its swiveling axis.

Turning now to the details of the construction above the base portion A,the last-named portion, at the upper part thereof, is provided with abed member 10 to support the turret B. The turret (FIG. 9) includes asleeve part 11 rotatably and concentrically mounted through antifrictionmembers on an inner upstanding tube part 12 fixed to the bed member 10.A ring gear 13, having internal teeth and of an internal diameterconsiderably in excess of the external diameter of the sleeve part 11,is arranged concentrically with respect to the sleeve part 11 and fixedto the upper surface of the bed member ltl. Twin metal brackets 24 ofelongated form are provided and bolted to the sleeve part 11 (FIG. 8),as at 15, the brackets having portions thereof extending laterally awayfrom the sleeve part 11 in parallel and spacedapart relation to oneanother, and being received in the end of a hollow arm 16 of generallyrectangular cross section, the brackets being secured thereto, as byfasteners 17, for support of the arm from the sleeve part 11.

In the preferred form of the invention, the arm 16 is constructed ofplastic material reinforced with glass fibers. The arm 16 extendsoutwardly and upwardly, as shown in FIG. 3. As shown in FIGS. 1 and 2,the armequipped turret is provided with a dome-like cover it;

which is removable and which is preferably constructed of the samematerial as the turret arm. Within the turret and mounted for rotationtherewith are two electric-motor-and-pump units, indicated generally at19, and supported from a bracket 20 also bolted to the sleeve part 11 ofthe turret by the bolts 15. One unit 19 operates the lower bloom sectionC, and the other unit 19 operates the upper boom section D in a mannerwhich will appear hereinafter. Electric-motor-and-gearing means H, whichdrives the turret, is also supported from the sleeve part 11. Thelast-named means, which is supported from a bracket 21 suspended fromone of the brackets 14 and secured thereto as at 22, includes anelectric motor 23 driving a pinion 24 through reduction gearing 25. Thepinion 24 meshes with the teeth of the ring gear 13 to drive the turret,and it will be manifest from the foregoing that the sleeve part 11, thearm 16, the motor-andpump units 19 and the electric-motor-and-gearingmeans H all rotate together as a unit.

At the other end thereof the arm 16 receives a transverse pivot shaft26, mounting the inner end of the lower boom section C. The pivot shaft26 extends through the inner end of the lower boom section, and this endof the last-mentioned boom section is arranged in sideby-side relationwith the outer end of the arm 16 as indicated in FIGS. 3 and 4. Thelower boom section, which is generally of tubular construction, isformed of plastic material reinforced with glass fibers and may be ofgenerally rectangular cross section. The pivot shaft 26, best shown inFIG. 5, is stationary and supports the lower boom section throughantifrication devices 27. An idler pulley 23 is rotatably mounted on theshaft 26 within the boom section C, as shown in the last-mentioned view,and also within the lower boom section and fixed to the shaft 26 inaxially spaced relation is a radially projecting arm 29. At the other,or outer, end of the lower boom section C, a pivot shaft Elli, mountingthe upper boom section D, extends transversely into the lastnamed boomsection from the same side of the boom section as the arm 16. The pivotshaft 30 is revoluble in the boom section C (FIG. 6) and equipped withsuitable antifriction devices.

The pivot shaft 26 is mounted in an integrally formed cap portion 31 ofthe lower boom section, which has a somewhat thickened wall structure(FIG. 3) and is closed on the end, as at 32. As shown in FIG. 3, the capportion as enlarged to extend below the tubular portion 33 of the boomsection and in this region has an opening 34 facing the outer end of theboom section. The cap portion (FIG. is internally reinforced, as at 35.The other end of the boom section C is provided with a similar capportion 36 mounting the pivot shaft 3%, as shown in FIG. 6. The capportion 36 is provided with an internal web 37 supporting the inner endof the pivot shaft 30. The pivot shaft 3%, which is hollow, has a flange33 bolted to the inner end of the outer boom section D. Mounted onantifriction devices for rotation within the pivot shaft 30 is a hollowshaft 39, extending beyond the ends of the shaft 30 and having withinthe cap portion 3?, and beyond the shaft 30 a radially extending arm 46fixed to the shaft 39. Within the lastnamed cap portion a pulley 41 isfixed to the pivot shaft 30. The shaft 39 extends within the boomsection D, which, like the boom section C, is of hollow construction,and within the boom section D the shaft 39 is provided with a splitpulley 42 fixed thereto by a pin 43, the sections (FIG. 6) of the splitpulley being adjustably bolted together, as at 44, to permit angularadjustment of one pulley section relatively to the other.

The upper boom section B is also constructed of plastic materialreinforced with glass fibers and, as shown in FIG. 3, the boom section Dis tapered to become progressively narrower in an outward direction, andat the outer extremity thereof is provided with an enlargement 45. Theinner end portion of the outer boom section D is internally reinforced,as at 46, as shown in FIG. 6. The enlarged outer end 45 of the boomsection D receives a laterally extending hollow pivot shaft 47 angularlyrigid with the work platform B. As shown in FIG. 7, antifriction devices48 are interposed between the shaft 47 and the boom section D. A pulley49 is fixed to the shaft 47 within the boom section D. The work platformE, which is of bucket-like construction for a workman to stand in, has asubstantially hollow lateral projection 5i mounting the shaft 47. Thebucketlike work platform also has a frontal recess 51 for manuallyoperated controls, controlling the boom structure and to be describedhereinafter. The bucket-like work platform, together with the extension50 and shaft 47, is formed of plastic material reinforced with glassfibers and, like the lower and upper boom sections, has a highdielectric strength to insulate a workman supported on the platform fromelectrical shock hazards, and also others, such as persons on or nearthe truck.

The hydraulic cylinder F, by which the lower boom is raised and lowered,has one end thereof (FIG. 3) pivoted to the turret arm 16, as at 52, atwhat may be termed the elbow of the arm 16, the pivot point being spacedbelow and somewhat to one side of the pivot shaft 26. The hydrauliccylinder has an extensible piston rod 53. A metal bracket 5 having apart extending through the wall structure of the tubular portion 33 ofthe lower boom section and fixed therein in a suitable manner, has apart projecting outwardly of and (FIG. 3) below the last-mentionedportion of the lower boom section and pivotally supporting the outer endof the piston rod 53, as at 55, a distance outwardly from the pivot 26,mounting the boom section C for vertical swinging movement. Thearrangement of the last-mentioned hydraulic cylinder is such that whenthe piston rod 53 is extended the lower boom section C is raised, andwhen the piston rod is retracted, this boom section is lowered.

As best shown in the last-mentioned view, the hydraulic cylinder G,operating the upper boom section, is supported from the lower boomsection intermediate the ends of the latter, the hydraulic cylinder Gbeing fixed to the lower boom section below the latter by brackets 56.The hydraulic cylinder G has a piston 57 and piston rods 58, one at eachside of the piston, to extend through the respective ends of thecylinder. One rod 58 is connected to one end of a cable 59, and theother rod 58 is connected to one end of a cable 6%). The cable 60 istrained over the idler pulley 28 and has the other end portion thereofwrapped around the pulley 41 and secured thereto in a conventionalmanner. The cable 59 is trained over the pulley 41 and has the other endthereof wrapped around the last-named pulley and secured thereto in aconventional manner.

The arrangement is such that when the cable 59 is pulled by thecorresponding piston rod 58 in a direction toward the inner end of theboom section, the upper boom section is swung upwardly through rotationof the pivot shaft 30. During this movement of the upper boom section D,the cable 59 is unlaid from the pulley 41 While the cable 60 is laid onthe last-mentioned pulley. It will be understood that when thelast-named piston rod is retracted to effect the last-named movement ofthe upper boom section, the other piston rod 58 is extended to permitthe cable 60 to move over the idler pulley 28 in a direction to be laidon the pulley 41. It will be manifest from the foregoing that the upperboom section D is lowcred through retraction of the piston rod 58connected to the cable 60 and it will be understood that during thismovement the cable 60 is unlaid from a pulley 41 while the cable 59 islaid on the last-mentioned pulley. The cable 60 extends into the boomsection through the opening 34 in the cap 31 while the cable 59 extendsinto the cap 36 in like manner. A channel-shaped housing 36 fixed to theboom section C and disposed below the latter,

as shown in FIG. 3, extends a distance inwardly from the cap 36 to coverand insulate a portion of the cable 59 and a part of the piston rod 58connected thereto.

A levelling mechanism is provided to maintain the bucket-like workplatform E in upright position during all swinging movements of thelower and upper boom sections. To this end a rod 61 pivotallyinterconnects the outer end of the arm 29 fixed to the stationary pivotshaft 26 and the outer end of the arm 4-9 fixed to the revoluble shaft39. The levelling mechanism includes the split pulley 42 from whichcables 62 and 63 pass outwardly in the outer boom section D. One endportion of the cable 62 is wrapped around one section of the splitpulley 42 and anchored thereto, and one end portion of the cable 63 iswrapped around the other pulley section and anchored thereto. The cables62 and 63 are interconnected through rods 64 and cables 65, as shown inFIG. 3.

As shown in the last-mentioned view, the rods 64, which may be ofsubstantial length and which are constructed of a material having a highdielectric strength, such as plastic reinforced with glass fibers,extend lengthwise in the upper boom section D. One rod 64 has the innerend thereof connected to the outer end of the cable 62, while the otherrod 64 has the inner end thereof connected to the outer end of the cable63. The other ends of the rods 64 are connected to the respective endsof the cable 65 which has the central or middle portion thereof wrappedaround the pulley 49 and trained over an idler 66 supported in the outerend portion of the boom section D adjacent the enlargement 45. The cable65 has the middle part of the portion thereof wrapped around the pulley49 anchored to the latter, as at 66 to resist slippage of the cable onthe pulley under normal operating conditions.

The operation of the levelling mechanism will be manitest from theforegoing disclosure. When the lower boom section C is at rest, as inthe position shown in FIG. 3, for example, and the upper boom section Dis raised, the link 61, interconnecting the arms 29 and 46, tends tomaintain the pulley 42 in stationary relation to the lower boom sectionC, and as the upper boom section D is raised from the position of FIG.3, that is, swung in a clockwise direction as viewed here, the cable 62is unlaid from the pulley 42, while the cable 63 is laid on thelast-mentioned pulley, and through movement of the cables 62 and 63,which control the rods 64 and the cable 65, the bucket-like workplatform is maintained in upright position. It will be understood thatthe cable 62' is laid and the cable 63 is unlaid when the upper boomsection D is lowered. When the lower boom section C is raised, thepulley 42 is rotated in a clockwise direction, as viewed in FIG. 3,through the link-controlled arm 29. This movement of the pulley 42relatively to the lower boom tends to maintain the bucket-like workplatform in upright position, and it will be understood from theforegoing that when the lower boom section C is lowered, the pulley 42is rotated relatively to the lower boom in opposite direction tomaintain the platform in upright position. Should the cable 65 slip onthe pulley 49, or should either of the cables 62 or 63 become slack, thesections of the split pulley 42 may be adjusted angularly to oneanother. This adjustment may be made to compensate for slippage of thecable 65 or to remove slack from the cables 62 and 63.

The base portion A of the boom structure is upwardly extensible toenable a workman on the work platform E to reach greater heights. Tothis end, the base portion A includes a parallelogram, best illustratedin FIGS. 13

and 14. The parallelogram is supported from the side frames 67 of thetruck which mount, in fixed relation thereto, transversely extendingmetal members 68 of,

channel construction, the last-named members being supported from theside frames 67 through fittings 69. The channel members 68 are notcentered on the truck frame,

but extend to one side, as shown in FIG. 14. A pair of arms 70 areprovided at the last-mentioned side of the truck and extend upwardlyfrom the respective channel members 68 in rigid relation thereto. Onelink of the parallelogram, which is of a platelike construction andwhich is indicated at 71, extends between the arms 70 for pivotalsupport from the outer ends of the arms, this link being provided withpivots 72 mounting the link for vertical swinging movement on the arms76. The companion link 73 of the parallelogram, which is of similarconstruction, extends between the channel members 68 in pivotal relationthereto, the link 73 being pivoted to the members 63, as at 74, inwardlytoward the center line of the truck from the arms 71 as indicated inFIG. 14. As shown in FIG. 13, the pivot 74 may be constituted by a rodextending through the channel members 68.

The other ends of the links 71 and 73' are pivoted to an elbow fitting,indicated generally at 75, which, as viewed in FIG. 14, is generally ofthe shape of an isosceles triangle having two short sides. Theplate-like links 71 and 73 are pivoted to one short side of the fitting75 in spaced-apart relation by pivots '76 similar to the pivots 72. Theelbow fitting 75 comprises two triangular side plates 77 laterallyspaced apart by a wall 78 extending between the long sides of thetriangles. The wall 78 and the side plates 77 are strengthenedby achannel member 7h extending along the wall 7 8 between the plates 77 andprovided with laterally spaced-apart lugs 80 for a purpose which willappear hereinafter. derstood from the foregoing that the links 71 and 73extend between the side plates 77.

Links 81 and $2 of the parallelogram, corresponding to the links 71 and73, respectively, each have one end pivoted to the other short side ofthe triangular fitting 75 by pivots 83 similar to the pivots 72, theseends of the links being spaced apart on the last-mentioned side of thefitting 75. The parallelogram includes a pair of channel members 84spaced apart lengthwise of the truck and similar to the channel'members68, the members 84 supporting therebetween in fixed relation the bedmember 10 of the turret B. A pair of arms 86, corresponding to the arms76, project downwardly from the respective channel members 84 at thesame side of the truck and the other end of the link 81 extends betweenthe lower ends of the arms 86 and is pivoted to the lastmentioned endsby pivots 87 similar to the pivots 72. The other end of the link 82extends between the channel members 84 above and inwardly toward thecenter line of the truck from the pivots 87, the last-named end of thelink being pivoted to the channel members 84 by a pivot 88, similar tothe pivot 74.

It will be manifest from the foregoing that regardless of the degree ofextension of the parallelogram the links 71 and 73 remain parallel toone another and the links 81 and 82 remain parallel to one another, tothereby maintain the turret-supporting members 84 in parallel relationto the frame of the truck. The parallelogram constitutes an elevator forthe turret B and is raised and lowered by hydraulic cylinders 89 and 96.For this purpose, the piston rod 91 of the hydraulic cylinder 89 may bepivoted on pivot 74 while the end of the cylinder may be pivoted betweenthe lugs 86' of the fitting 75, as at 92. The hydraulic cylinder 6 mayhave the piston rod 93 thereof pivoted on pivot 38 while the end of thecylinder may be pivoted to the fitting 75, as at 94, between the lugs86. As indicated in FIG. 13, the platelike links of the parallelogramare suitably recessed to provide clearance for the swingaole hydrauliccylinders 89 and 96. The arrangement is such that the parallelogram maybe extended on extension of the piston rods 91 and 93 and folded onretraction of these rods. Furthermore, it will be manifest that thehydraulic cylinder 39 serves to swing the links 71 and 73 and thehydraulic cylinder 96 operates the links 81 and 82. It is important, aswill appear hereinafter, that the hydraulic cylinders- It will be un- 89and 90 may be operated independently of one another. For this purpose,an extensible control member, indicated generally at 95, is provided.

The extensible control member 95 in the illustrated form includes (FIGS.13 and 14) tubular elements, 96, 97 and 98 in telescoping relation toone another, the ele ment 98 telescoping into the element 97 and thelatter telescoping into the element 95. Only the elements 97 and 98 areextensible. The control member 95 is vertically arranged and the upperend of the element 96 is pivoted for vertical swinging movement, as at99, to an upstanding arm 100 rigidly supported on one of the channelmembers 84. A fitting 101 on the truck, the fitting being shown on oneof the channel members 68, is connected to the element 98 and supportsthe latter for swinging movement with the elements 96 and 97. Thefitting 101, which prevents axial movement of the element 98, provides apivot which is of the fixed type. It will be manifest from the foregoingthat the control member 95 is extended when the parallelogram orelevator moves from the lower broken-line position of FIG. 14 to theupper broken-line position of this view, and it will be understood thatthe control member 95 is telescoped when the parallelogram is folded.

The control member 95 carries adjacent the lower end thereof a mercuryswitch mechanism 102, the mercury bulbs of which, together with theelectrical connections of which, are best indicated in FIG. 15. Thefunction of the control member is to control, through tipping movementof the mercury switch mechanism 102, the operation of the hydrauliccylinders 89 and 90 to maintain the weight of the parallelogram betweenthe wheels of the truck and thereby inhibit the tendency of this weightto tip the truck sideways. This is especially important when the truckis, itself, tipped to some extent due to the slope or unevenness of theground, a very common operating condition. The switch mechanism 102 issupported for swinging movement on the lower end of the element 98. Itwill be understood from the foregoing that, if the piston rod 91 isextended and operated independently of or at a faster speed than thepiston rod 93, the tendency is to move the turret bed to the left of thetruck, that is, left as viewed in FIG. 14. If the piston rod 93 isextended and operated independently of or at a faster speed than thepiston rod 91, there is a tendency to shift the turret bed to the rightof the truck. The swingable mercury switch mechanism 192 controls thesetendencies to inhibit tipping forces on the truck during the raising andlowering of the parallelogram and, furthermore, as will appear morefully hereinafter, the switch mechanism 102 eifects shifting movement ofthe upper end of the parallelogram to the left or the right tocompensate for unevenness or slope of the ground on which the truck issupported.

The parallelogram folds to be substantially centered on the truck bodywhen in the stowed position illustrated in broken lines in FIG. 14. Inorder to achieve this, the lower pair of links of the parallelogram musthave their lower pivotal connections to one side of the center line ofthe truck. Thus when the truck is level, as shown in FIG. 14, and theparallelogram is extended to its greatest height, shown in broken linesin the last-mentioned figure, the center of the turret bed must be tothe right of the center line of the truck in order to efiect a center ofgravity between the wheels of the truck. As indicated in FIG. 15, theswitch mechanism 1112 carried by the swingable control member 95includes two mercury bulbs, one indicated at 103 and the other at 104.The mercury bulb 103 controls the hydraulic cylinder 90 when and as theparallelogram is extended and controls the hydraulic cylinder 89 whenand as the parallelogram is folded. The mercury bulb 104 controls thehydraulic cylinder 89 when and as the parallelogram is extended andcontrols the hydraulic cylinder 90 when and as the parallelogram isfolded. These mercury bulbs control,

through the circuitry shown in FIG. 15, a pair of electrically operatedvalves 105, one valve being interposed in each pair of fluid linesprovided for the hydraulic cylinders 89, 91), the two-way hydrauliclines connected to the hydraulic cylinder 89 being indicated at 196 andthe corresponding lines for the hydraulic cylinder 90 being indicated at197'. It will be understood from the foregoing disclosure that it isextremely advantageous to control the movements of the parallelogram soas to shift the center of gravity to the left or the right and therebycompensate for sideways tilt of the truck due to sloping or unevenground. It will be manifest from the foregoing that the parallelogram orelevator may have many uses apart from its use to elevate turretcarriedboom sections.

To enable the parallelogram to be completely folded for stowage on thetruck under conditions where the truck is tipped sideways due to theslope of the roadway, for example, a switch 108 is mounted (FIG. 14), ason one of the side frames 67 of the truck, to be tipped by impingementwith the parallelogram as the latter is folded, the switch 108 effectingthe by-passing of the switch mechanism 102 as shown in FIG. 15.

As indicated in the last-mentioned view, a reversible electricallyoperated motor and pump 109 is provided to supply hydraulic fluid underpressure to the cylinders 89, 90 which operate the parallelogram. Thismotor and pump unit, similar to the motor and pump units 19 which arealso reversible, is mounted (FIG. 2) for stationary support from thetruck frame. As shown in FIG. 15 of the drawings, the hydraulic cylinderP, which operates the lower boom section C, is connected to one motorand pump unit 19 through two-way hydraulic lines 110, while thehydraulic cylinder G, which operates the upper boom section D isconnected to the other motor and pump unit 19 through two-way hydrauliclines 111. The reversible motor 23, which drives the turret in eitherdirection through previously described gearing, is also indicated in thelast-mentioned view. The unit 109, like the units 19 and the reversiblemotor 23, may be operated either from the control unit 112 mounted inthe frontal recess 51 of the bucket-like work platform or a control unit113 mounted (FIG. 1) on the truck body. In the preferred form thecontrol unit on the work platform is of the pneumatic type to furtherreduce electrical shock hazards to workmen, the last-mentioned controlunit being connected to the pump motors and the motor 23 throughflexible tubes 114- passing through the boom sections and formed of adielectric material such as plastic. For this purpose eight tubes 114are provided and eight air-transmitting mechanisms 115 of the manuallyoperated type, constructed identically to the mechanism 115 shown inFIGS. 10 and 11, are connected within the bucket-like work platform tothe respective upper ends of the tubes 114. The control mechanisms 115are arranged in pairs so that the units 19, the motor 23 and the unit109 may be operated in either direction. Eight air-receiving mechanisms116, identical to the mechanism 116 shown in FIG. 12, are provided atthe lower ends of the respective tubes 114.

The air-transmitting mechanisms 115 are supported from a common panel117 through which each has a part extending for manipulation. Eachtransmitting mechanism 115 (FIG. 10) has a cup-like lower part 118having, in the side wall structure thereof and near the bottom, an inletand outlet 119, and having, in the center of the bottom, an air outlet129. A vertically arranged bellows 121 is disposed in the bottom portionof the cup part 118 and has an upper end fitting 122 in fixed relationto the bellows and a lower end fitting 123 also secured to the bellows.The fitting 122 closes the upper end of the bellows except in thecentral region thereof and in this region the fitting 122 has anupwardly extending tubular part 124, providing an opening communicatingwith the interior of the bellows 120. The upper extremity of the tubularpart 124 is tapered, as at 125, and, as best shown in FIG. 11, thistapered portion is provided with a circumferential groove 126 seating anO-ring gasket127 forming a valve seat.

The lower fitting 123 closes the lower end of the bellows except in thecentral region thereof and in this region is internally threaded toreceive a nipple 123 on the corresponding air line 114, the nippleextending into the cup part 118 through the air outlet 129. The fitting123 has in communication with the last-named threaded part a tubularpart 129 extending upwardly in the bellows and opening into the latter.As shown in FIG. 10, the lower end of the bellows is rather narrowlyconfined between the tubular part 129 and the cup part 118. The upperend of the part 118 is filled by an insert 130 secured to the side wallstructure of the part 113 as by screw 131. The insert 130, which has acentral bore 132 therethrough enlarged at the lower end by a counterbore113, has a peripheral shoulder 134 to abut the upper edge of the cuppart 118. As shown in FIG. 11, the tubular part 124 of the upper bellowsfitting may be extended with clearance into the counterbore 133.

Above the cup part 118, the insert 133 has a reduced externally threadedportion 135 threaded upwardly through the panel 117 for support by thelatter, and the upper end of the portion 135 receives a nut 136 over awasher which bears against the top of the panel 117. A plunger 135,which extends loosely into the portion 132 so that air may passlengthwise along the plunger, has an enlargement 139 at the lower endthereof to abut the bottom of the counterbore 133 and thereby preventseparation of the plunger from the insert 130 on upward movement of theplunger. As shown in FIG. 10, the enlargement 139 of the plunger isconsiderably smaller in diameter then the side wall of the counterbore133. The plunger 138 normally extends a distance above the insert 131)and at the upper end thereof is provided with a disk 141) securedthereto and providing a button to move the plunger downwardly upon handpressure of an operator thereagainst. A flexible cover 141, of thewellknown accordion type, embraces the plunger 138. The cover has oneend thereof suitably fixed to the upper part of the plunger below thedisk 141i and has the other end disposed over the nut 136.

The enlargement 139 of the plunger has a conical recess 143 in thebottom thereof approximating the taper of the portion 125 of :thetubular part 124, the last-named recessed part forming a valve forseating engagement with the valve seat 127. The upper end fitting 122 ofthe bellows 121 normally occupies the position shown in FIG. 11. Withinthe cover 141 a compression spring 141 is provided, acting between thenut 136 and the disk 1413, and embracing the plunger 138. The lastnarnedspring, which may be omitted if the cover 141 is sufficiently resilient,normally maintains the plunger 138 in (the position of FIG. 11. In thisposition, the plunger is spaced upwardly :from the upper end fitting ofthe bellows 121 to permit air'to enter or escape from this bellow andthe corresponding air line 114. When the button 140 is depressed throughhand pressure, the plunger 138 seats on the upper end fitting of thebellows, cutting oil the entry of air to the bellows, and compresses thebellows to transmit, through the line 114, air under pressure to thecorresponding air-receiving mechanism 116 such as that shown in FIG. 12.

Each air line 114 at the lower end thereof has a nipple 14-5 connectingthe line to a fixed end (FIG. 12) of a bellows 146 forming a part of thecorresponding airreceiving mechanism 116, the last-named end being fixedby a bracket 147. The nipple communicates with the interior of thebellows 146, and the other or movable end of the bellows 146 is closedby a fitting 14-8 including a plunger 149 extensible into thecorresponding switch 151) (one switch 150 being provided for eachair-receiving mechanism 116) to engage and move a spring biased leafmember 151. The leaf member 151 has a contact 152 and is biased in adirection toward a fixed contact 153 to normally engage the latter withthe contact 152. The leaf member 151, with is a conductor and has aterminal 151 is provided with a contact 154 for-cooperation with a fixedcontact 155. When the bellows 146 is extended by air pressure from theair line 114, the plunger 149 is extended to engage and move the leafmember 151 in a direction to break the electrical connection between thecontact 153 and the terminal 151 and establish an electrical connectionbetween the contact 155 and the terminal 151 through the contact 154. itwill be understood from the :fioregoing that when the button 148 isreleased by the operator, the bellows 121 is permitted to re-expand,moving the plunger 133 upwardly. This results in contraction of thebellows 146 which retracts the plunger 143, allowing the biased leafmember 151 to disengage the contact 155 and re-establish the electricalconnection between the contact 153 and the terminal 151 through thecontact 152. It may be notedthat, as shown in FIG. 12, within the casingof the switch 155 the plunger is provided with an enlargement 1419forming an abutment for engagement with the casing to prevent separationof the plunger from the switch casing.

In the diagram of FIG. 15, the air-transmitting mech- I anism 115 whichcontrols raising of the lower boom section is indicated at 157, thecontrol mechanism 115 for lowering this section at 158, the mechanism115 for raising the upper boom section at 159, the mechanism 115 forlowering the upper section at 16% the mechanism 115 for raising theparallelogram at 161, the mechanism 115 for lowering the parallelogramat 16 2, the mechanism 115 for rotating the turret in one direction at163, and the mechanism 115 for rotating the turret in the oppositedirection at 164. As the operating connections between the controlmechanisms 115 and the respective electrical motors are identical, onlythe connections of those controls 163 and 164- will be described.

When the operating plunger of the control mechanism 163 is depressed bythe operator on the Work platform, the contacts 152 and 153 of thecorresponding switch are separated to render the control mechanism 164inoperative, and the contacts 154- and are closed to complete a circuitfirom a source of power such as a generator (not shown) driven from thetruck engine. This circuit includes a positive line 165 and a negativeline 155. The closing of this circuit energizes a relay including anelectromagnet 167 which closes contacts 168 and 169 to establish acurrent through line 176 to the turret motor 23. The motor is energizedand rotated in one direction as the current passes through the motor andout line 171. When the operating plunger of the control mechanism 163 isreleased by the operator, the circuit through the motor is broken byseparation of the contacts 154 and 155. The contacts 152 and 153 arethen reclosed.

When the operating plunger or the control mechanism 164 is depressed bythe operator, the contacts 152 and 153 of the corresponding switch 153are separated to render the control mechanism 163 inoperative, and thecontacts 154- and 155 are closed to complete the circuit through lines165 and 166 to energize an eleotromagnet 172 which closes contacts 173and 174- to establish a current through line 175 to the turret motor 23.The motor 23 is energized and rotated in the opposite direction ascurrent passes through the motor and out line 171. When the operatorreleases the operating plunger of the control mechanism 164, the circuitthrough the motor 23 is opened through disengagement or" the contact 154with the contact 155. It will be-understood from the foregoing that thecontrol mechanisms 163 and 164 are of the deadman type.

It has been previously indicated that when the parallelogram is raised,the electrically operated valve 1135 controlling the cylinder 91? iscontrolled by the mercury bulb 193 and the electrically operated valve1&5 controlling the cylinder 89 is controlled by the mercury bulb 104,and that the control of these valves by the bulbs is switched when theparal-leogram is folded. This is accomplished in the manner set forthbelow.

When the operating plunger of the control mechanism 162 is depressed tolower or fold the parallelogram, a circuit 177 is established toenergize an electromagnet 178. The magnet 178 breaks the line 179, m at181 and establishes a line 181, as at 182, while breaking the line 183,as at 184, and establishing line 185, as at 136. This connects themercury bulb 103 with the electrically p erated valve 105 controllingthe cylinder 89 and connects the mercury bulb 164 with the electricallyoperated valve 1&15 controlling the cylinder 9t Also as indicated inFIG. 15, the control unit 113 mounted on the truck body includes fourmanually operable switches 187, one switch 187 controlling each of theaforementioned electrical motors through either of the electro-magnets167 and 172 associated therewith.

In the form of the boom structure shown in FIGS. 16 and 17 the turret,the lower boom section, the upper boom section and the bucket-like workplatform are the same as those described above. The form of FIGS. 16 and17, unlike the form of FIGS. 1 through 15, has the turret-carried boomsections thereof supported on a stationary base part, that is, theparallelogram or elevator is omitted. In the modified form the rotaryturret is mounted on the suitably reinforced canopy 189 of the truck inaxially fixed relation thereto. It will be manifest from the foregoingthat the boom structure of FIGS. 16 and 17 is unable to reach theheights which may be reached with the first-descnibed form of the boomstructure.

As shown in FIGS. 16 and 17, the boom structure may be provided with aremovable auxiliary boom, indicated generally at 191 which, while notlimited thereto, is especially useful for raising and placing utilitypoles in upright position. The boom 1% comprises three pole members, twoof the last-named members constituting a pair and each being indicatedat 191, and the third pole member being of somewhat ditferentconstruction and being indicated at 192. The pole members 191 and 192are arranged in triangular relation as indicated in FIGS. 16 and 17 andin the position of the boom 199, shown in FIG. 16, extend upwardly andlaterally. As indicated in the last-mentioned view, the pole members 191are arranged in the same upward plane, the members 191 having theirlower ends (FiG. 17) spaced apart and having their upper end portions inconverging relationship. Each of the members 191 is constituted by atleast two telescoping 1 sections 193, 11 4- for relative lengthwiseadjustment, the sections being releasably locked in their adjustedposition, as by pins 195 passing through both sections. The pole member192 is constructed of similar relatively telescoping sections 196 and197 adjustably locked together in the same manner. The upper end of thepole member 192 extends between the upper ends of the pole members 191and the three pole members are pivotally interconnected in this region,as by a pivot pin 198.

The lower ends of the pole sections 193 are apertured to be removablymounted on the threaded studs 199 extending therethrough substantiallyon the pivotal axis of the lower boom section C. Nuts 290 may bethreaded on the respective studs by hand to removably secure these polesections in place. As indicated in FIG. 17, one stud 199 extendslaterally from the lower boom section C, while the other stud 199extends in the opposite direction from the turret arm 16, the studsbeing supported from the pivot 26. A distance outwardly of the lowerboom section from the pivotal axis of the last-mentioned section, abracket 201 is secured to the side of the boom section C nearest the arm16 and is provided with an aperture to removably receive a threaded stud232 which extends transversely through the lower end of the pole section197 and which may be removably secured to the bracket 12 201 by a nut203 similar to the nuts 200, as indicated in FIG. 17. When the auxiliaryboom 19!) is secured in place as described above, the outer end of thisboom may be projected laterally by upward swinging movement of the lowerboom section from the position of FIG. 16, and

it will be manifest from the foregoing that this end of the boom may beraised by lowering the last-mentioned boom section.

A lifting cable is indicated at 204. This cable is trained over a pulley205 supported on the pivot pin 198 and is provided at its outer end witha cable fitting 206. The cable 204 runs downwardly along the pole member192 and is trained over a pulley 207 suitably supported on the lowerboom section C. The cable 2&4 passes downwardly from the pulley 207through the central part of the turret and into the truck body where itis wound on a motor driven winch 208 of conventional design and equippedwith conventional controls, not shown.

A pulley 2119 (FIG. 16) within the truck body may cooperate with thecable 294 between the turret and the winch 298, and a fitting 210 isremovably supported on the top of the turret to cooperate with the runof the cable between the pulleys 207 and 209 to prevent the cable frombeing rubbed on the turret. The fitting 210 is of upstanding tubularconstruction and at the upper end thereof is provided with pulleys 211and 212 arranged in diametrically opposite relation to one another. Whenthe lower boom section C is in the position shown in FIG. 16, the cablecooperates with the pulley 211. However, when the last-named boomsection is raised from this position, the cable 21% leaves the pulley211 and enters the pulley 212.. The construction and arrangementprovides a very satisfactory hoist which is one of the advantages of theboom structure.

It will be manifest from the foregoing disclosure that a furtheradvantage common to both forms of the boom structure resides in theconstruction and arrangement of the boom sections and their support onthe arm of the turret. In this connection it may be pointed out thatwhen the lower boom section is projected across the turret from the arm16, as shown in FIG. 16, and the upper boom section is raised, thetipping forces on the truck occasioned by the weight of the boomstructure are materially reduced. It will be understood that the boomsections will not corrode due to their construction of reinforcedplastic material and require little, if any, maintenance work.Furthermore, these boom sections have a very high dielectric strength toprotect workmen from electrical shock hazards. Still further, inconnection with electrical shock hazards, it will be noted that theupper boom section has no conductor for electrical current extending thelength thereof. The boom sections and the turret arm do not have metalcore members extending throughout their length to transmit shocks andthe very length of the boom sections and the turret arm serve asadditional electrical insulation from shock hazards. As previouslyindicated, pneumatic tubes 114 which run through the boom sections areformed of dielectric material, and the rods 64- within the upper boomsection and which form a part of the levelling mechanism are alsoconstructed of dielectric material. All lines to the work platform runwithin the boom sections throughout their lengths except where theselines pass through the hollow pivot shafts. The pneumatic lines whichcontrol the movements of the boom structure are of the self-chargingtype due to the construction and arrangement of elements in theair-transmitters 115. Due to the provision of the conically recessedvalve seats 143 of these transmitters, condensation is prevented fromdripping into the apertured upper end fittings 122 of the bellows 121which form terminal connections of the air lines. The normally open airlines permit air to enter or leave them through the port 119 in each airtransmitter which port also serves to permit the escape of moisture fromwithin the transmitter. The normally open air lines permit air to escapeas when iii the lines are subjected to heat, and permit air to enter thelines, as when the lines are subjected to cold temperatures.

Another feature of the boom structure resides in the simplification ofthe levelling mechanism for the work platform and the adjustability ofthis mechanism. -An advantage of the canopy mounting of the boomstructure, shown in FIGS. 16 and 17, resides in the mounting of the boomstructure in such away that the truck bed is left free for the stowageof accessory equipment, for example. A further advantage of thestructure resides in the improved means for swinging the upper boomsection on its pivotal axis through an arc of substantially 270 degrees.It will also be manifest that the use of the parallelogram or elevator,which may be mounted to fold lengthwise of the truck instead oftransversely thereof, if desired, may add to the heights attained by theboom structure by many feet while maintaining tipping forces on thetruck at a relatively low level or degree so that stabilizing Outriggersare unnecessary on the truck.

Important advantages are obtained through the use of the boom actuatingmechanisms and controls therefor illustrated and described above. Inthis connection it is notatable that the operating mechanism requires aminimum number of valves, owing to the use of reversible electricmotors. Furthermore, motors are operated only during movements of theboom structure, and not continuously as in most hydraulic controlmechanisms for boom structures of this general type. The use ofelectrical motors in mechanisms to move parts of the boom structure,such as the elevator, turret and boom sections, enables these parts tobe moved smoothly without abrupt starts and stops. In this connection itmay be noted that while the controls for the motor are of thesingle-speed type, the motors do not attain maximum speed at thecommencement of their operation nor stop at maximum speed. This makesfor smoother operation of the boom structure.

till another feature of the boom structure is that it may be stowedeasily on a truck within a relatively small space. In this connection itmay be noted that the boom structure does not require the use of verylong boom sections to reach substantial heights but employs an elevatorfor this purpose which may fold transversely of the truck and verycompactly. The mounting of the lower boom section on the laterallyprojecting arm of the turret so that this section may be folded acrossthe turret also facilitates stowage of the boom structure on a truck.

While only two forms of the boom structure have been illustrated anddescribed above, it will be apparent to those versed in the art that theboom structure may take other forms and is susceptible of many changesin details without departure from the principles of the invention andthe scope of the claims.

What I claim is:

1. In a mobile aerial tower, a truck, a support element, means mountingthe support element on the truck to elevate and project it to eitherside of the truck, a turret rotatable on a substantially vertical axison said support element, a boom pivoted to the turret for verticalswinging movement, a workers platform supported from the outer end ofsaid boom, means for operating said firstnamed means and for operatingthe turret and said boom, and means including gravity-responsive meansinterconnecting said support element and said truck to limit, onprojection of said support element, the lateral extension of saidsupport element and the degree of said projection Within a pr determinedlimit of the height of elevation of said support element from the truckin accordance with substantially the center of gravity of the truck,tending to prevent tipping over of the truck.

In a mobile aerial tower, a truck, parallel linkages mounted on thetruck, a support element, the support element and the truck beinginterconnected by said linkages, and said support element beingprojectable to either side of the truck and vertically, a turretrotatable on a subi i stantially vertical axis on said support element,a boom pivoted to the turret for vertical swinging movement, a workersplatform supported from the outer end of said boom, means for operatingsaid boom and the turret and for operating said linkages, and meansincluding gravityresponsive means, cooperating with said first-namedmeans, operatively interconnecting the truck and said support element tolimit the degree of projection of said support ele ment from the truckin accordance with substantially the center of gravity of the truck,tending to prevent tipping over of the truck on projection of saidsupport element through said linkages.

3. In a structure of the class described, a base member which may assumea tipped position, a plurality of pairs of links forming aparallelogram, the pairs being pivotally interconnected in end-to-endrelation and the parallelogram being supported at one end from the basemember for vertical and lateral extension therefrom, the other end ofthe parallelogram having a load-lifting and -shifting member thereonmaintained in parallelism with the base'member through said pairs oflinks, linkage-swinging means to swing adjacent pairs of the links inopposite directions and independently of one another to thereby raiseand laterally relocate the position of the support member with referenceto the base member, and self-operating control means acting on saidlinkage-swinging means to control the direction and extent of lateralrelocation of the support member to thereby offset tipping forces on thebase member as the parallelogram is extended, said control meansincluding movable gravity-responsive control members and an elementsupported from the load-- lifting and -shifting member, the last-namedelement being operative to move and reorient said gravity-responsivemembers in accordance with the shifting of the base member relatively tothe load-lifting and -shifting member as the parallelogram is extended,said last-named element having a pivotal connection in fixed relation tothe loadlifting and -shifting member and carrying the gravityresponsivemembers, and said element of the control means having a further swingingaxis, which axis is in fixed relation to the base member, the last-namedelement being of a telescoping construction and being extensible on theextension of the parallelogram.

4. In a mobile boom structure, a truck having a canopy, a rotary turretmounted on top of the canopy and having a central passage therethroughcommunicating with an opening in the top of the canopy, the turret beingmounted for svvivelling movement on a vertical axis and having aload-supporting arm projecting upwardly and laterally therefrom, aload-lifting-and-supporting boom having the inner end thereof pivotallymounted on the outer end of said load-supporting arm for swingingmovement of the boom in a vertical plane across the turret, means foreffecting swinging movement of the boom, an auxiliary boom of tripodconstruction fixed to theinner end portion of the first-named boom andprojecting outwardly therefrom substantially at right angles to the axisof the first boom for swinging movement therewith, the tripod having thefoot of one leg secured to the first boom a distance outwardly from thepivotal connection of the latter to the arm, a flexible elongated hoistmember running over the outer end of the auxiliary boom and runningdownwardly into the truck canopy through said passage in the turret,means to guide the run of said hoist member into the turret, and a winchwithin the truck canopy and on which the hoist member may be wound andunwound.

5. In a levelling mechanism for a work platform carried at the outer endof an articulated boom structure having two boom sections, the innerboom section being swingable through an arc ofapproximately degrees andthe outer boom section being swingable through an arc of approximately270 degrees, a first pivot supporting the inner end of'the inner boomsection, a second hollow pivot angularly rigid with the inner end of theouter boom section and swingably mounting the outer section on the outerend of the inner section, a third pivot mounting the platform on theouter end of the outer boom section, the third pivot being fixed to theplatform and having a pulley fixed thereon, a fourth pivot extendingthrough the second pivot and being rotatable therein, the fourth pivotat one end of the second pivot having a pulley fixed thereto, a singlelink extending along the lower boom section and connecting at one endwith the fourth pivot at the other end of the second pivot, the otherend of the link having a fixed axis adjacent and parallel to the axis ofthe first pivot, and means interconnecting said pulleys and includingcable portions, said link effecting angular adjustments of the platformon swinging movements of the lower boom section, and the last-namedmeans effecting angular adjustments of the platform on swingingmovements of the upper boom section.

References (Iited in the file of this patent UNITED STATES PATENTSHennessey Mar. 16, Bryant et a1 Nov. 7, Hetzelberger July 26, Smith Nov.19, Conrad Apr. 5, Gerli et a1. Mar. 14, Curtis Oct. 21, Stemm Nov. 4,Wagner Oct. 23, Bramming Mar. 19, Meagher Jan. 21, Troche Apr. 7, TrocheDec. 1, Hall May 17, Richey June 14,

1. IN A MOBILE AERIAL TOWER, A TRUCK, A SUPPORT ELEMENT, MEANS MOUNTINGTHE SUPPORT ELEMENT ON THE TRUCK TO ELEVATE AND PROJECT IT TO EITHERSIDE OF THE TRUCK, A TURRET ROTATABLE ON A SUBSTANTIALLY VERTICAL AXISON SAID SUPPORT ELEMENT, A BOOM PIVOTED TO THE TURRET FOR VERTICALSWINGING MOVEMENT, A WORKER''S PLATFORM SUPPORTED FROM THE OUTER END OFSAID BOOM, MEANS FOR OPERATING SAID FIRSTNAMED MEANS AND FOR OPERATINGTHE TURRET AND SAID BOOM, AND MEANS INCLUDING GRAVITY-RESPONSIVE MEANSINTERCONNECTING SAID SUPPORT ELEMENT AND SAID TRUCK TO LIMIT, ONPROJECTION OF SAID SUPPORT ELEMENT, THE LATERAL EXTENSION OF SAIDSUPPORT ELEMENT AND THE DEGREE OF SAID PROJECTION WITHIN A PREDETERMINEDLIMIT OF THE HEIGHT OF ELEVATION OF SAID SUPPORT ELEMENT FROM THE TRUCKIN ACCORDANCE WITH SUBSTANTIALLY THE CENTER OF GRAVITY OF THE TRUCK,TENDING TO PREVENT TIPPING OVER OF THE TRUCK.